In GPON/EPON ONU, both types of patch cords are using according to the interface of ONU
Generally, most of China OEM (Original equipment manufacturer) choosing SC/PC optical interface for their ONU/ONT. For such products, it’s only possible to use SC/PC patch cords.
Even though, if the product integrated with CATV (cable tv )service, it has SC/APC interface. For such products need to use SC/APC patch-cords.
But some OEM chooses SC/APC optical interface for all their products ranges. In those interfaces only SC/APC patch cord is suitable.
We can easily define the right patch-cord by understanding the ONU optical interface color. SC/APC shown as green and SC/PC shown as Blue color. Few products, the patch cord is directly connecting to ONU transceiver (shown as a different color than green or blue), there we can use SC/PC.
If we use the different patch cord, the physical contact will occur high insertion loss than normal. That may affect the performance of the service. Also the CATV ONU, always suggest following with SC/APC to avoid direct reflection to ONU laser.
Do you know what is the essential optical input level of a CATV passive node?